Unable to select a PO line in a existing Trade Operation

Summary:

The user has an existing Trade Operation with the charges lines and the PO. But in some of the lines of the PO they reversed the receipt of the PO, also that PO's lines has the invoices. When they change that, they want to associate again the lines of the PO in existing Trade Operation, the system don't take that's PO line. What is the cause?

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